Material handling vehicles, and particularly automatic guided vehicles (AGV's) of the driverless type are typically utilized for transporting loads between work stations and storage locations. Such vehicles have a load carrying deck which is provided for supporting the load. Frequently, such decks are elevationally movable for positioning the deck at an appropriate height to receive a load or to lift a load located above the deck. AGV's and in particular self guided vehicles (SGV's), vehicles which have free ranging capabilities and do not require wires, stripes or other fixed guide paths, are sensitive to load distribution and require the load to be placed precisely on the vehicle so that the on-board vehicle sensors used for guidance purposes receive accurate readings of the actual position of the vehicle. For example, if the load is offset, the loading of the vehicle wheels will be unequal and this will cause unequal compression of the tires and a slight deviation in the rolling radius of the wheels from the calculated value. This will result in an error in the location of the vehicle calculated from information received from the wheel sensors. As operating time continues the error will increase and eventually the vehicle will be unable to perform load acquisition and deposit activities. Therefore, it is important that the load be positioned on the vehicle accurately.
Frequently, the load carried on the vehicle is retained on the deck by restraining devices such as spaced-apart gates, stops and the like. These restraining devices are provided to keep the load on the deck and from falling off the deck during vehicle operation. The restraining devices normally permit different sizes of loads to be positioned therebetween and this may allow for excessive movement of smaller dimensioned loads on the deck during vehicle operation. Because of this movement, the load may not be able to be positioned close enough to the storage rack, conveyor, machine tool and the like to permit transfer. It is therefore important that the load be accurately retained on the vehicle to overcome this problem.
The load to be transported is often carried on a load supporting device, such as a pallet, rack, table or the like which is greater in width than the width of the vehicle. In such applications, the load supporting device is often not positioned on the vehicle so that the extension of the load past the sides of the vehicle are equal. In this position the center of gravity of the load will be transversely offset from the center of gravity of the vehicle. During vehicle operation the moment of the offset load acting on the vehicle will cause vehicle bounce, vehicle leaning and the like. Thus, the accuracy of vehicle guidance, load positioning, and efficiency of operation will suffer.
Vehicles such as AGV's and SGV's often operate in narrow aisle environments. These vehicles are normally guided for movement down the center of the aisle and in close proximity to the sides of the aisle. Therefore, an offset load on the vehicle which extends past one of the vehicle sides more than necessary will reduce the amount of aisle space available and the tolerance in navigation error that can be accommodated. Thus it is important that the load supporting device be accurately located on the vehicle and restrained from movement in directions transverse to the vehicle.
Fixed conical devices have been provided on vehicles having elevationally movable decks to allow a portion of the vehicle deck to float so that it may be aligned with a conveyor, machine tool and the like and to restrain the vehicle deck portion during vehicle travel by engaging the cones with cups on the deck portion. A separate restraint and positioning device is provided since these conical devices do not position and restrain the load supporting device on the vehicle deck. This adds to the complexity and cost of the vehicle.
In situations where the load supporting device is to be lifted from an underlying supporting surface it would be inappropriate to provide fixed cones on the deck of the vehicle and pilot bores in the load supporting device. During elevation of the deck the cones would first engage the bores and drag the load supporting device along the underlying surface until the load was centered relative to the vehicle. This loading would apply forces to the lifting deck and the vehicle in directions transverse the elevational movement of the deck and cause adverse loading of the deck and of the vehicle. This side loading would result in a reduction in the life of the load carrying deck and the vehicle. In situations where the weight of the load on the load supporting device is substantial, the vehicle, instead of the load, may be moved. This would greatly reduce the accuracy of operation of an AGV or SGV and eventually result in error so great that alignment and the continuance of vehicle operation would be impossible. The present invention is directed to overcoming one or more of the problems as set forth above.